1. Field of the Invention
The present invention is directed to a shock wave generator of the type suitable for use in an apparatus for non-contacting disintegration of calculi in the body of a life form, and in particular to such a shock wave generator having an electrically conductive membrane which is activated by a coil having windings disposed adjacent to the membrane.
2. Description of the Prior Art
A shock wave generator is disclosed in German OS No. 33 28 051 having, corresponding to U.S. Pat. No. 4,674,505, an electrically conductive membrane arranged parallel to a coil. Shock waves are generated by connecting the coil to a high voltage supply which has a capacitor charged to several kilovolts, for example 20 kV. The energy stored in the capacitor is suddenly discharged into the coil, so that the coil rapidly generates a magnetic field. Simultaneously, a current is generated in the membrane, the current being opposite to the current flowing in the coil. The current in the membrane thus generates an opposing magnetic field, causing the membrane to be suddenly moved away from the coil. The membrane terminates a volume which is filled with a shock wave conducting medium, such as fluid, by means of which the shock wave generated by the membrane movement is focussed to the calculi, for example, kidney stones, disposed in the body of a life form. Such focussing is accomplished with suitable means known to those skilled in the art, and causes disintegration of the calculi.
In order to achieve an optimal conversion of the electrical energy emitted by the high voltage supply into shock wave (impact) energy, conventional shock wave generators of the type described above require the membrane to be disposed as close as possible to the coil. Because of the difference in potential which necessarily exists between the coil and the membrane (which corresponds to the magnitude of the high voltage because the membrane is at ground in common with a terminal of the coil and a pole of the high voltage supply), the closeness of the membrane to the coil is limited because a minimum spacing must be observed in order to avoid voltage arcing between the membrane and the coil. Voltage arcing would deteriorate the effectiveness of the shock wave generator, and also leads to damage of the membrane, resulting in a shortened useful life thereof. In conventional shock wave generators, therefore, the distance between the coil and the membrane must be selected as a compromise in view of maintaining an adequate useful life of the membrane such that an unsatisfactory efficiency in the conversion of electrical energy into impact energy results.